The invention relates to a method of conveying imprint material, particularly solar cells, from a processing area of a flatbed printing machine, by which the imprint material is first positioned on a first conveyer belt section, by which the imprint material is then processed and by which the imprint material on the first conveyer belt section is then moved further out of the processing area. The invention also relates to a method of imprinting plates of imprint material, particularly solar cell wafers. The invention further relates to a printing table for a flatbed printing machine, particularly for the screen printing of solar cell wafers, having a conveyor belt for conveying imprint material from a processing area of the printing table during processing, the imprint material resting on a first conveyor belt section, and having at least one driving device for moving the conveyor belt over the printing table.
According to the invention, a method is provided for conveying and imprinting a sensitive imprint material as well as a printing table for sensitive imprint material, particularly a thin solar cell wafer or thin glass.
According to the invention, a method of conveying imprint material, particularly solar cells, from a processing area of a flatbed printing machine is provided, having the following steps: Positioning the imprint material on a first conveyor belt section of a conveyor belt in the processing area, processing the imprint material, further moving the imprint material on the first conveyor belt section out of the processing area, automatically checking of the first conveyor belt section for soiling or damage and, as a function of the checking result, further positioning the imprint material on the first conveyer belt section or moving a second conveyor belt section into the bearing area.
Using an exemplary method according to the invention, it can be ensured that imprint material positioned in the processing area will rest on a clean conveyor belt section which is not soiled or damaged. Specifically in the case of a sensitive imprint material, for example, of solar cells or thin glass susceptible to breaking, it may happen that the wafer breaks during the imprinting of the strip conductors. Even after the removal of this broken wafer, it is probable that splinters or printing paste may still adhere to the conveyor belt, which leads to the danger that wafers processed subsequently will also be soiled or damaged. According to the invention, the first conveyor belt section is automatically checked for soiling or damage and, as a function of the result of the checking step, is either used again for the bearing of imprint material, or a second clean conveyor belt section is moved into the bearing area. This ensures that no splinter, residues or printing paste or the like are present on the conveyor belt section on which the imprint material is conveyed into the processing area. The conveyor belt consists, for example, of a paper web. As a function of the result of the checking step, a soiled or damaged paper web section is rolled up and no longer used. On the other hand, if the paper web section is not soiled or damaged, it will be used again. Particularly in the case of continuous processes for high numbers of pieces, this process reduces the paper web consumption and especially the downtimes for the reloading of the paper web can be considerably decreased.
As a further development of the invention, the first conveying section may be moved back into the processing area as a function of the checking result. In this case, the checking of the first conveyor belt section takes place outside the processing area, for example, below the processing area. If it is determined in that the first conveyor belt section is damaged, a second conveyor belt section is already situated on the printing table in the processing area.
As a further development of the invention, the first conveyor belt section may be moved back into the processing area and, depending on the result of the checking step, a second conveyor belt section may be moved into the processing area.
In this case, the checking of the first conveyor belt section takes place in the processing area, so that monitoring cameras can be arranged above or diagonally above the processing area. Thus, if the first conveyor belt section is determined to still be good and continuously usable, no further conveyor belt movement would be required because the first conveyor belt section had been moved back into the processing area even before the check.
A further embodiment of the invention provides an automatic checking of the processed imprint material for damage or soiling in the processing area and, as a function of the checking result, the further processing of the imprint material and the removal of the imprint material from the processing operation.
For example, if a solar cell wafer breaks during the imprinting, the latter has to be removed from the processing operation. In this situation, further checks may be automatically triggered, which determine the integrity of the conveying and printing devices.
In a further embodiment of the invention, the imprint material may be imprinted in the processing area by means of screen printing and, after the imprinting, an automatic checking of a printing screen may take place for damage or soiling. If the checking finds damage or soiling, the printing screen may be removed by means of a scraper or the like.
For example, in the event of broken solar cell wafers during the imprinting, splinters may adhere to the printing screen, which would make also subsequent printing operations faulty, or destroy the screen mesh printing stencil. It is therefore advantageous, if necessary, to also check the printing screen after the imprinting for damage or soiling, depending on results of the checking step, and if necessary, to scrape the printing screen by means of a scraper or the like in order to remove splinters or soiling therefrom. The printing screen may be advantageously moistened before, during or after the removal in order to partially detach undesirable residues from the printing screen.
In a further embodiment of the invention, after the imprinting of the imprint material and after the automatic checking of a printing screen following the imprinting, free-printing of the printing screen onto the first conveyor belt section and movement of a second conveyor belt into the processing area may be carried out as a result of the checking operation.
Especially when splinters or other soiling materials adhere to the printing screen, the latter can generally be cleaned again by free-printing. According to the invention, free-printing takes place in a particularly simple manner on the first conveyor belt section, and subsequently a clean second conveyor belt section is moved into the processing area. Particularly advantageously, this can also be used when the conveyor belt is constructed as a paper web. However, it will be understood that one may use other conveyor belts which are not necessarily usable only once. For example, the then imprinted first conveyor belt section may be part of a revolving conveyor belt and can be cleaned in a cleaning station and then can be used again.
As a further embodiment of the invention, a printing image of the free-printing on the first conveyor belt section may be checked automatically. By checking the printing image after the optionally repeated free-printing, contamination or damage to the printing screen can be determined. The checking takes place, for example, by means of cameras and an image processing unit on the output side. The free-printing can, for example, be repeated until the printing image during the free-printing indicates an undamaged and clean printing screen.
As a further embodiment of the invention, the checking of the printing screen may be initiated as a function of the result of an automatic checking of the processed imprint material.
For example, checking of the printing screen may be initiated only if the imprint material was damaged during the printing operation. For example, imprinted solar cell wafers may be checked for fracturing by a transmitted-light method and, as a function of the result of this check, if a fracturing of the wafer is determined the printing screen may be checked for contamination and damage.
According to the invention, an exemplary method of imprinting imprint material plates, particularly solar cell wafers, by means of a screen printing machine, includes the following steps: aligning of at least two imprint material plates relative to one another, positioning of the at least two mutually aligned imprint material plates in the processing area of the screen printing machine, for example on a conveyor belt, and simultaneous processing the at least two imprint material plates and further moving the at least two imprint material plates out of the processing area, for example on the conveyor belt.
The exemplary method provides a double benefit or even multiple benefits since two or more imprint material plates can be simultaneously processed on a single printing table and by means of a single printing screen. Since the printing operation itself is comparatively time-consuming, a very high throughput can be achieved in this manner, which is extremely advantageous, for example, in the mass production of solar cell wafers. In this case, it is preferred that the at least two imprint material plates are aligned relative to one another so that in the mutually aligned condition they can then be positioned on the conveyor belt in the processing area of the screen printing machine. Thus, the imprint material plates are thereby aligned with respect to the printing screen, but the printing screen itself may no longer have to be aligned. The normally required alignment of the printing screen with respect to the imprint material therefore can be eliminated. By using the alignment of the printing screen, only an exact positioning relative to one of the at least two imprint material plates could be achieved. However, according to the invention, the two imprint material plates are deposited on the imprint material bearing device already in a mutually substantially aligned manner, and are therefore already in the correct position such that the printing takes place simultaneously onto the at least two imprint material plates through the printing screen.
However, the printing screen can also still be aligned. This may be necessary in the event that the printing screen was not placed correctly by means of a 3-point contact in the machine, or when faults during the screen production are to be compensated.
As a further embodiment of the invention, the alignment of the at least two imprint material plates comprises lifting the at least two imprint material plates and moving them relative to one another in the lifted condition.
In this manner, the imprint material plates, such as sensitive solar cell wafers, can be aligned relative to one another in a device in the lifted condition, and the imprint material plates therefore do not have to be displaced on a base and be placed, for example, against stops. In the lifted condition, a very precise mutual alignment of the imprint material plates can thereby be achieved while being handled very carefully. The imprint material plates, which are exactly aligned with respect to one another, are then deposited on the printing table in the exactly intended position and are therefore already correctly aligned with respect to the printing screen. As a result, the two imprint material plates situated side-by-side can be imprinted with a high precision by means of a single printing screen. A double benefit is again achieved, and it is further possible to process more than two imprint material plates in this manner in order to achieve a multiple benefit.
As a further embodiment of the invention, at least two imprint material plates are checked simultaneously. If some solar cell wafers are determined to be in poor condition, other solar cell wafers that are assessed to be good are moved into a parked position, while the solar cell wafers evaluated to be poor are sorted out.
In this manner, at least two imprint material plates can be processed simultaneously. After the check, the solar cell wafers are lifted and, in the lifted condition, are then aligned relative to one another. In order to be able to process the supplied groups having of at least two imprint material plates, faulty imprint material plates are sorted out, while the remaining good imprint material plates are first parked. When additional imprint material plates are again evaluated as bad, a complete group of imprint material plates evaluated as good can be assembled again.
As a further embodiment of the invention, the processed imprint material plates are dried in a run-through dryer, at least two imprint material plates being arranged side-by-side on a conveyor belt of the run-through dryer.
Providing a run-through dryer with a conveyor belt permits the easy transfer of imprinted imprint material plates to the conveyor belt, without having to lift the imprint material plates once again. In order to achieve a high throughput in the dryer, at least two groups of imprint material plates are respectively arranged side-by-side on the conveyor belt. When, for example, two solar cell wafers are simultaneously imprinted, ten imprinted solar cell wafers may be arranged side-by-side in the run-through dryer and are moved through the run-through dryer.
As a further embodiment of the invention, the printing screen may be lifted and/or swiveled during the printing operation. By means of such a screen lift, a clean printing image is achieved due to the lifting of the printing screen, because when the printing screen is lifted off the imprint material after the imprinting of a respective location, a printing squeegee is moved over it.
The embodiments of the present invention include a printing table for a flatbed printing machine, particularly for the screen printing of solar cell wafers, having a conveyor belt for the conveying imprint material, for example out of a processing area of the printing table. During this processing, the imprint material resting on a first conveyor belt section passed along at least one driving device for moving the conveyor belt over the printing table, a checking device for checking at least the first conveyor belt section for contamination and damage after a further conveying of the imprint material, and a control unit. The control unit controls the at least one driving device as a function of the checking result of the checking device, such that either the first conveyor belt section is moved back into the processing area after the further conveying of the imprint material, or a second conveyor belt section is moved back into the processing area. However, generally only two solar cell wafers may be moved directly side-by-side through the dryer. This has the advantage that additional operating steps can be eliminated.
Using the printing table according to the invention, it can be ensured that a clear and undamaged conveyor belt is always available for the processing of sensitive imprint material.
As a further embodiment of the invention, the conveyor belt may be constructed as a paper web. Paper to use in a conveyor belt is available at reasonable cost, so that damaged sections can be disposed of. However, as explained above, by using the embodiments of the invention, the paper web consumption is nevertheless significantly minimized. Furthermore, a paper web can hold possibly leaked printing ink so that additional printing machine parts will not be soiled.
As a further embodiment of the invention, viewed in the conveying direction, rollers can be provided on both sides of the printing table for the rolling-up or unrolling of the conveyor belt.
In this manner, large quantities of conveyor belt material, such as a paper web, can be held in the clean as well as in the soiled condition, so that in connection with the multiple utilization of the paper web sections according to the invention, downtime for exchanging the conveyor belt can be significantly reduced.
As a further embodiment of the invention, at least one of the rollers may be arranged to be movable relative to the printing table bearing surface.
As a result of the movable arrangement of at least of one of the rollers, a movement of the first conveyor belt section downward from the printing table bearing surface or upward onto the latter can take place without a rotation of this at least one roller. Specifically, at least one of the rollers is swiveled or displaced in order to move the first conveyor belt section out of the processing area on the printing table bearing surface, and to then mount this first conveyor belt section away from the printing table bearing surface, particularly in a flat manner. On the one hand, the first conveyor belt section can thereby be checked for soiling and damage outside the printing table bearing surface. On the other hand, it can be achieved that the at least one roller always only has to be moved in the same rotating direction. This is particularly important when there is the danger that printing ink or other more or less strongly adhering substances reach the conveyor belt. When both rollers are fixedly and non-displaceably mounted, in order to move the first conveyor belt section downward from the printing table bearing surface and then to move it back again, both rollers first have to be moved into one rotating direction and then into the other rotating direction. If an adhering substance such as printing ink or printing paste for strip conductors arrives on the conveyor belt, especially the paper web, a paper web section soiled by the printing paste eventually may be wound onto a paper web section already situated on the roller, which paper web section is also already soiled by printing paste. This situation may lead to a thorough moistening of the paper web and possibly to a tearing of the paper web. It may also lead to a gluing-together of the stacked paper web layers. In a worst case, this condition leads to a blocking of the entire paper web. This is not the case according to the embodiments of the invention, wherein at least one of the rollers, specifically the roller onto which the soiled paper web is wound, is always only rotated in one direction, and wherein paper web sections soiled by the still moist printing paste are also wound on one another. However, these paper web sections then no longer have to be separated from one another, so that a possible gluing-together of the paper webs is of no consequence.
As a further embodiment of the invention, at least one of the rollers may be displaceably disposed in guide rails.
For example, at least one of the rollers can be displaceably disposed in guide rails arranged vertically with respect to the printing table surface. This roller, onto which the soiled paper web is wound, can then keep the paper web tensioned as a result of its own weight. When the additional roller situated on the opposite side of the printing table bearing surface dispenses a length of conveyor belt, this roller is displaced by its own weight downward along the vertically arranged guide rail. The first conveyor belt section from the processing area thereby becomes flat and is mounted outside the printing table bearing surface and, as required, may be checked for soiling and damage. When the conveyor belt is again wound onto the opposite roller, this roller is then pulled upward again along the guide rails. This is also the case when this exemplary roller is caused to rotate to wind-up soiled paper belt. The roller, which is to receive the soiled conveyor belt and which is disposed in the vertical guide rails, therefore only has to be able to rotate in one rotating direction and may be provided, for example, with a free-wheel.
As a further embodiment of the invention, the checking device has at least one camera and image processing devices.
The conveyor belt can be checked by means of a camera and, as required, by means of varied lighting. Lighting can take place, for example from above, laterally or from below. Suitable image processing devices can detect damage or soiling of the conveyor belt and, as a function of the checking result, can trigger a driving device for the conveyor belt such that a new clean and undamaged conveyor belt section reaches the processing area.
As a further embodiment of the invention, the conveyor belt can have an air-permeable construction, and the printing table bearing surface can be provided with intake openings for the application of a vacuum.
A paper web may, for example, have a blotting-paper-like and therefore air-permeable construction in order to hold sensitive imprint material on the printing table during the printing operation, without the risk of damage, and reliably and with the required precision.
As a further embodiment of the invention, an elastic intermediate layer, particularly a rubber layer, may be arranged between the conveyor belt and the printing table bearing surface.
Particularly in the case of very sensitive imprint material, for example solar cell wafers, which are extremely susceptible to fracturing and which at the same time are not completely flat, an elastic intermediate layer can further reduce the risk of fracturing during the printing operation.
For example, a silicone rubber layer may be arranged below the conveyor belt, and may be provided with passage bores in the raster of the intake openings provided in the printing table.
As a further development of the invention, a cleaning device can be provided which has a scraper or similar element for cleaning a printing screen. The cleaning device advantageously also has a moistening element for moistening the printing screen.
By means of such a cleaning device, it can be ensured, for example, after the fracturing of a solar cell wafer, that splinters or other dirt that would impair subsequent printing operations, no longer adhere to the printing screen. After the lifting of the printing screen, the cleaning device with the scraper or the similar element is moved along the underside of the printing screen and thereby scrapes ink residues and splinters possibly adhering to the ink residues off the printing screen. A moistening of the printing screen can partially detach possible residues during the cleaning.
Additional characteristics and advantages of the invention are found in the claims and the following description in connection with the drawings. Individual characteristics of the different embodiments can also be combined arbitrarily without exceeding the scope of the invention.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.